Prepared for the U.S. Army Corps of Engineers, Kansas City District
August 1981

Abstract

Saltwater contaminates the alluvial aquifer of the Smoky Hill River valley and then discharges into the river to the east of Salina, Kansas. The brine derives primarily from groundwater solution of the Hutchinson Salt Member and associated gypsum and anhydrite of the Permian Wellington Formation. During Federal and State studies to assess reducing mineral intrusion to the river, a question arose as to whether oil,-field brine could also be polluting the aquifer. Before substantial control regulations were promulgated, oil-field brines were disposed in surface pits and in disposal wells in evaporite solution cavities of the Wellington Formation, as well as in deeper formations. Some disposal is still allowed in the Wellington Formation.

The sources of salt in the groundwaters were identified by sodium/ chloride ratios and curves of bromide/chloride and iodide/chloride versus chloride concentration for mixtures of fresh waters and brines in the area. Magnesium/chloride, lithium/chloride, and boron/chloride ratios helped verify sources. These methods showed no detectable oil-field brine entering the alluvium from shallow aquifers along the valley walls. Either surface disposal pits were little used in the area or any past pollution has not moved appreciably or has been flushed by recharge. However, a few observation wells in the saline Wellington aquifer contained varying mixtures of oil-field and evaporite solution brines. A USGS well pumped to test interception of saltwater in the Wellington Formation produced predominantly halite solution brine.

Over 40 percent of the recharge volume needed to balance the average discharge of saltwater from the Wellington Formation to the Smoky Hill River is presently being injected as oil brine into the Wellington, mainly in south-central Saline County and north-central McPherson County. The total volume injected since 1940 amounts to only about one percent of the total saltwater in the brine aquifer. The disposed oil brine will probably take roughly 100 years before first discharging into the river. Increases in piezometric head from the brine injection have probably already spread to the discharge area. Saltwater disposal into the Wellington Formation should be abandoned as soon as practical to prevent further recharge and increase in piezometric head.

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